UnlockFileEx function (fileapi.h)

Article
02/22/2024

Unlocks a region in the specified file. This function can operate either synchronously or asynchronously.

Syntax

BOOL UnlockFileEx(
  [in]      HANDLE       hFile,
            DWORD        dwReserved,
  [in]      DWORD        nNumberOfBytesToUnlockLow,
  [in]      DWORD        nNumberOfBytesToUnlockHigh,
  [in, out] LPOVERLAPPED lpOverlapped
);

Parameters

[in] hFile

A handle to the file. The handle must have been created with either the GENERIC_READ or GENERIC_WRITE access right. For more information, see File Security and Access Rights.

dwReserved

Reserved parameter; must be zero.

[in] nNumberOfBytesToUnlockLow

The low-order part of the length of the byte range to unlock.

[in] nNumberOfBytesToUnlockHigh

The high-order part of the length of the byte range to unlock.

[in, out] lpOverlapped

A pointer to an OVERLAPPED structure that the function uses with the unlocking request. This structure contains the file offset of the beginning of the unlock range. You must initialize the hEvent member to a valid handle or zero. For more information, see Synchronous and Asynchronous I/O.

Return value

If the function succeeds, the return value is nonzero.

If the function fails, the return value is zero or NULL. To get extended error information, call GetLastError.

Remarks

Unlocking a region of a file releases a previously acquired lock on the file. The region to unlock must correspond exactly to an existing locked region. Two adjacent regions of a file cannot be locked separately and then unlocked using a single region that spans both locked regions.

Locks are released before the CloseHandle function is finished processing.

In Windows 8 and Windows Server 2012, this function is supported by the following technologies.

Technology	Supported
Server Message Block (SMB) 3.0 protocol	Yes
SMB 3.0 Transparent Failover (TFO)	Yes
SMB 3.0 with Scale-out File Shares (SO)	Yes
Cluster Shared Volume File System (CsvFS)	Yes
Resilient File System (ReFS)	Yes

Requirements

Requirement	Value
Minimum supported client	Windows XP [desktop apps \| UWP apps]
Minimum supported server	Windows Server 2003 [desktop apps \| UWP apps]
Target Platform	Windows
Header	fileapi.h (include Windows.h)
Library	Kernel32.lib
DLL	Kernel32.dll